Electronically generated perspective images

ABSTRACT

A method and system for electronically generating and displaying shaded perspective images of three-dimensional objects on a twodimensional view plane by providing electrical signals representative of the surfaces of an object and identifying and utilizing only the signals representing visible surfaces to display the perspective images. More specifically, electrical signals defining surfaces of a three-dimensional object are converted to define the projections of the surfaces onto a twodimensional image or view plane defined by a raster scan display device. The converted signals defining surfaces which are to be displayed, depending on the desired orientation of the object, are determined by comparing the relative depths of segments of the surfaces along each scan line of the display and selectively subdividing the scan lines according to the visual characteristics of the segments when necessary. Signals defining the visible segments are then utilized to control the intensity of the display. The visibility determination and subsequent displaying of the visible surfaces are provided at a real time rate, i.e., at the scanning rate of the display which may be on the order of 1/30 second.

United States Patent ll l Watkins [451 May 29, 1973 154] ELECTRONICALLY GENERATED PERSPECTIVE IMAGES Gary S. Watkins, Salt Lake City, Utah [73] Assignee: University of Utah, Salt Lake City,

Utah

22 Filed: June 1,1971

21 Appl.No.: 148,801

[75] Inventor:

[52] U.S. Cl. ..340/172.5, 340/324 A, 235/151 [51] Int. Cl. ..G06f 15/20, 606g 7/48 [58] Field of Search ..340/172.5, 324 A;

[56] References Cited UNITED STATES PATENTS 3,145,474 8/1964 Taylor, Jr. ..340/172.5 X

3,454,822 7/1969 Harrison ..340/324 A 3,418,459 12/1968 Purdy et al. ....340Il72.5 X 3,519,997 7/1970 Bernhart et al ....340/172.5 3,523,289 8/1970 Harrison ...340/324 A 3,527,980 9/1970 Robichaud et al ...340/324 A 3,539,860 11/1970 Max et al ..340/324 A 3,602,702 8/1971 Warnock ....340/l 72.5 X 3,621,214 11/1971 Romney et al ..340/172.5 X

OSCILLOSCOPE AND CAMERA COORDINATE Primary Examiner-Paul J. i-lenon Assistant Examiner-Melvin B. Chapnick Attorney-Lynn G. Foster [57] ABSTRACT A method and system for electronically generating and displaying shaded perspective images of threedimensional objects on a two-dimensional view plane by providing electrical signals representative of the surfaces of an object and identifying and utilizing only the signals representing visible surfaces to display the perspective images. More specifically, electrical signals defining surfaces of a three-dimensional object are converted to define the projections of the surfaces onto a two-dimensional image or view plane defined by a raster scan display device. The converted signals defining surfaces which are to be displayed, depending on the desired orientation of the object, are determined by comparing the relative depths of segments of the surfaces along each scan line of the display and selectively subdividing the scan lines according to the visual characteristics of the segments when necessary. Signals defining the visible segments are then utilized to control the intensity of the display. The visibility determination and subsequent displaying of the visible surfaces are provided at a real time rate, i.e., at the scanning rate of the display which may be on the order of 1130 second.

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1. A method for generating a perspective view display of a three-dimensional object on a two-dimensional raster scan display comprising the steps of: a. providing input data defining surfaces of the object to be displayed; b. generating segment data defining segments of the surfaces existing along the scan lines of the display responsively to the input data; c. determining the visibility of the segments existing within sample spans selected along the scan lines of the display; and, d. displaying the segments determined to be visible within the sample spans.
 2. The method of claim 1 wherein the step of determining the visibility of the segments existing within selected sample spans includes selectively subdividing those sample spans within which more than one segment is determined to be visible.
 3. The method of claim 2 wherein the sample spans extend between two sample points selected along the scan lines, the sample points including at least the edges of the display.
 4. The method of claim 3 wherein the sample points include the edges of segments determined to be visible along a previous scan line.
 5. The method of claim 4 wherein a sample span within which more than one segment is determined to be visible is selectively subdivided by moving the rightmost sample point to coincide with the leftmost segment edge existing between the sample points when at least one segment edge exists therebetween.
 6. The method of claim 5 wherein a sample span within which two segments are determined to be visible and within which no segment edges exist is selectively subdivided by calculating the point of intersection between the two segments and moving the rightmost sample point to coincide with the calculated point of intersection.
 7. The method of claim 6 wherein a sample span within which more than two segments are determined to be visible and within which no segment edges exist is selectively subdivided by moving the rightmost sample point to coincide with the mid-point of the sample span.
 8. The method of claim 1 wherein the visibility of the segments existing within a selected sample span is determined by: comparing the relative depths of the segments to determine if more than one segment is visible within the sample span when more than one segment exists within the sample span; and, selectively subdividing the sample span until only one visible segment exists in a subdivision thereof responsively to the relative depth comparison.
 9. The method of claim 8 wherein the relative depth of the segments existing within a sample span are compared by: selecting left and right clipping points defining at least a portion of the sample span; successively subdividing the segments relative to the selected clipping points; and, comparing the relative depths of the subdivided segments after each successive subdivision.
 10. The method of claim 9 wherein the segments are successively subdivided relative to the selected clipping points until a predetermined relationship exists between the clipping points and the subdivided segments or until it is determined that only one visible segment exists between the clipping points responsively to the relative depth comparison between the subdivided segments.
 11. The method of claim 8 wherein the sample spans extend between two sample points selected along the scan lines, the sample points including the edges of the display and edges of segments determined to be visible along a previous scan line.
 12. The method of claim 11 wherein a sample span within which more than one segment is determined to be visible is selectively subdivided by moving the rightmost sample point to coincide with the leftmost segment edge existing between the sample points when at least one segment edge exists therebetween.
 13. The method of claim 12 wherein a sample span within which two segments are determined to be visible and within which no segment edges exist is selectively subdivided by calculating the point of intersection between the two segments and moving the rightmost sample point to coincide with the calculated point of intersection.
 14. The method of claim 13 wherein a sample span within which more than two segments are determined to be visible and within which no segment edges exist is selectively subdivided by moving the rightmost sample point to coincide with the mid-point of the sample span.
 15. The method of claim 1 wherein the segment data is generated by: generating edge data defining the edges of the surfaces of the object to be displayed; ordering the edge data according to the scanning pattern of the display; and, generating the segment data responsively to the ordered edge data.
 16. The method of claim 15 wherein the step of determining the visibility of the segments existing within selected sample spans includes selectively subdividing those sample spans within which more than one segment is determined to be visible.
 17. The method of claim 16 wherein the sample spans extend between two sample points selected along the scan lines, the sample points including at least the edges of the display.
 18. The method of claim 17 wherein the sample spans include the edges of segments determined to be visible along a previous scan line.
 19. The method of claim 15 wherein the visibility of the segments existing within a selected sample span is determined by: comparing the relative depths of the segments to determine if more than one segment is visible within the sample span when more than one segment exists within the sample span; and, selectively subdividing the sample span until only one visible segment exists in a subdivision thereof responsively to the relative depth comparison.
 20. The method of claim 19 wherein the relative depth of the segments existing within a sample span are compared by: selecting left and right clipping points defining at least a portion of the sample span; successively subdividing the segments relative to the selected clipping points; and, comparing the relative depths of the subdivided segments after each successive subdivision.
 21. The method of claim 20 wherein the segments are successively subdivided relative to the selected clipping points until a predetermined relationship exists between the clipping points and the subdivided segments or until it is determined that only one visible segment exists between the clipping points responsively to the relative depth comparison between the subdivided segments.
 22. The method of claim 19 wherein the sample spans extend between two sample points selected along the scan lines, the sample points including the edges of the display and edges of segments determined to be visible along a previous scan line.
 23. The method of claim 22 wherein a sample span is selectively subdivided responsively to the relative depth comparison by: moving the rightmost sample point to coincide with the leftmost segment edge existing between the sample points when at least one segment edge exists between the sample points; calculating the point of intersection between the segments existing between the sample points when two segments are visible within the sample span and when no segment edges exist between the sample points; and, moving the rightmost sample point to coincide with the mid-point of the sample span when more than two visible segments are visible within the sample span and no segment edges exist between the sample points.
 24. A method for generating a perspective view display of a three-dimensional object on a two-dimensional raster scan display comprising the steps of: a. providing input data defining surfaces of the object to be displayed; b. generating segment data defining segments of the surfaces existing along the scan lines of the display responsively to the input data; c. comparing the relative depths of the segments existing within sample spans selected along the scan lines to determine if more than one segment is visible within the selected sample spans wherein more than one segment exists; d. selectively subdividing the sample spans wherein more than one visible segment is determined to exist; and, e. displaying the segments determined to be visible within the sample spans and the subdivisions thereof.
 25. The method of claim 24 wherein the relative depths of the segments existing within a sample span are compared by: selecting left and right clipping points defining at least a portion of the sample span; successively subdividing the segments relative to the selected clipping points; and, comparing the relative depths of the subdivided segments after each successive subdivision.
 26. The method of claim 25 wherein the segments are successively subdivided relative to the selective clipping points until a predetermined relationship exists between the clipping points and the subdivided segments or until it is determined that only one visible segment exists between the clipping points responsively to the relative depth comparison between the subdivided segments.
 27. The method of claim 24 wherein the sample spans extend between two sample points selected along the scan lines, and wherein a sample span within which more than one segment is determined to be visible is selectively subdivided by moving the rightmost sample point to coincide with the leftmost segment edge existing between the sample points when at least one segment edge exists therebetween.
 28. The method of claim 27 wherein a sample span within which two segments are determined to be visible and within which no segment edges exist is selectively subdivided by calculating the point of intersection between the two segments and moving the rightmost sample point to coincide with the calculated point of intersection.
 29. The method of claim 28 wherein a sample span within which more than two segments are determined to be visible and within which no segment edges exist is selectively subdivided by moving the rightmost sample point to coincide with the mid-point of the sample span.
 30. A real time method of converting input data into output data, said input data describing the surfaces of a three-dimensional object, said output data describing only the visible surfaces of the object projected onto a two-dimensional view plane established according to a desired orientation of the of the object, said method comprising the steps of: a. providing a view plane comprising a predetermined number of vertically spaced, substantially coextensive and substantially horizontal lines; b. generating segment data defining segments of the projected surfaces existing between edges of the projected surfaces along each horizontal line; c. selecting a predetermined number of sample points along each horizontal line; d. determining the number of visible segments existing between the selected sample points by comparing the relative depths of the segments as measured in a direction perpendicular to the view plane that exist between selected sample points along each horizontal line; f. selectively subdividing the portions of the horizontal lines that are defined by the selected sample points if more than one visible segment exist between the selected sample points; and g. generating output data defining a visible segment when the relative depth comparison indicates that only one segment is visible between the sample points or the subdivisions thereof.
 31. In a method for generating a perspective view display of a three-dimensional object on a two-dimensional raster scan display device from input data definIng surfaces of the object converted into projected surface data representing the surfaces of the object projected onto a two-dimensional view plane established according to the desired orientation of the object, said method including determining which of the surfaces represented by the projected surface data are to be displayed, and modifying the brightness of the display according to the projected surface data representing the surfaces determined to be displayed, the improvement wherein the surfaces to be displayed are determined and displayed in real time for each frame of the raster scan display device by: generating edge data from the projected surface data, the edge data representing edges of the projected surfaces; generating segment data defining continuous segments of the projected surfaces existing along each scan line responsively to the edge data; comparing the relative depths of the segments defined by the segment data along each scan line to generate visible segment data; and modifying the brightness of the raster scan display responsively to the visible segment data.
 32. A method for determining the relative visibility of two line segments projected onto a predetermined two-dimensional view plane along a line of intersection between the view plane and a plane perpendicular to the view plane, said line segments being coplanar and lying in a plane perpendicular to the view plane, each of said line segments being specified by two X end valves specified in the view plane and two Z end values specified in the plane perpendicular to the view plane, said method comprising the steps of: a. selecting a sample span between two sample points along said line of intersection; b. comparing the relative depths of the line segments existing between the sample points to determine which line segment is visible between the sample points; c. selecting a new sample span by moving the left sample point to coincide with the right sample point and by selecting a new right sample point; and d. repeating steps b) and c) until the visibility of all portions of said line segments has been determined.
 33. A method for determining the relative visibility of two line segments projected onto a predetermined two-dimensional view plane along a line of intersection between the view plane and a plane perpendicular to the view plane, said line segments being coplanar and lying in a plane perpendicular to the view plane, each of said line segments being specified by two X end values specified in the view plane and two Z end value specified in the plane perpendicular to the view plane, said method comprising the steps of: a. selecting a sample span between two sample points along said line of intersection; b. comparing the X end values of said line segments with the values of said sample points to determine if any of said X end values lie between said sample points; c. moving the rightmost sample point to coincide with the leftmost X end value of said line segments existing within the selected sample span if an X end value is determined to exist therein; d. comparing the relative depths of the line segments existing between the sample points to determine which line segment is visible between the sample points; e. selecting a new sample span by moving the left sample point to coincide with the right sample point and by selecting a new right sample point; and f. repeating steps b) through e) until the visibility of all portions of said line segments has been determined.
 34. A system for generating perspective images on a two-dimensional raster scan display of three-dimensional objects comprising: a. object creation means for generating first electrical signals representative of the three-dimensional object to be displayed; b. means responsive to said first electrical signals for generating second electrical signals corresponding to line segments of surfaces of said object which exist along scan lines of said display; c. means responsive to said second electrical signals for determining which line segments existing within a sample span selected along a particular scan line of the display are visible; and d. circuit means connecting signals from said visibility determining means to said display to generate a perspective image of said three-dimensional object.
 35. The system of claim 34 wherein said visibility determining means includes a further means for selectively subdividing any sample spans within which more than one segment is determined to be visible.
 36. The system of claim 35 wherein the sample spans extend between two sample points selected along the scan lines, the sample points including at least the edges of the display.
 37. The system of claim 36 wherein the sample points include the edges of segments determined to be visible along the previous scan line.
 38. The system of claim 35 wherein the means for determining the visibility of line segments along a particular scan line further includes: means for comparing the relative depths of the segments to determine if more than one segment is visible within the sample span when more than one segment exists within the sample span; and means responsive to said comparative depth determination means for selectively subdividing the sample span until only one visible segment exists in a subdivision thereof.
 39. The system of claim 38 wherein the means for determining relative depth of the segments existing within a sample span further comprises: circuit means for selecting left and right clipping points defining at least a portion of the sample span; means responsive to the selected clipping points to successively subdivide the segments relative to such selected clipping points; and means responsive to signals generated after each successive subdivision for comparing the relative depths of the subdivided segments.
 40. The system of claim 39 wherein said depth comparison means comprises a circuit arrangement for successively subdividing said segment relative to said clipping points until a predetermined relationship exists between the clipping points and the subdivided segments or until it is determined that only one visible segment exists between the clipping points.
 41. A system for generating perspective images on a two-dimensional raster scan display of three-dimensional objects comprising: a. object creation means for producing a first set of digital signals representative of said object; b. storage means for receiving said first set of digital signals; c. a pre-scan calculator connected to said storage means for retrieving said first set of digital signals and changing them in accordance with the desired orientation of the object to produce a second set of digital signals; d. a display device; e. means coupled to said pre-scan calculator for receiving said second set of digital signals and generating edge data signals defining the edges of the surfaces of the object to be displayed; f. means responsive to the edge data signals for ordering the edge data according to the scanning pattern of the display device; g. means responsive to the ordered edge data signals for generating further electrical signals corresponding to segments of lines in surfaces of said object which exist along scan lines of said display; h. means responsive to said further electrical signals for determining which segments of lines existing along a particular scan line of the display are visible; and i. circuit means connecting signals from said visibility determining means to said display device to generate a perspective image of said three-dimensional object.
 42. The system of claim 41 wherein the visibility determining means includes means for examining the data existing between two sample points along a scan line within selected sample spans in said line and means for selectively subdividing those sample spans within whicH more than one segment is determined to be visible.
 43. The system of claim 42 wherein the sample spans include the edges of segments determined to be visible along the previous scan line and the sample points include at least the edges of the display.
 44. The system of claim 41 wherein the visibility determining means includes: means comparing the relative depths of line segments within a selected sample span to determine if more than one segment is visible within said sample span when more than one segment exists within the sample span; and circuit means responsive to signals from said relative depth comparison means for selectively subdividing the sample span until only one visible segment exists in a subdivision thereof.
 45. The system of claim 44 wherein said relative depth comparison means further comprises: means selecting left and right clipping points defining at least a portion of the sample span; means responsive to the selected clipping points for selectively subdividing said segments relative to said clipping points; and further circuit means responsive to the signals from said successively subdividing means for comparing the relative depth of the subdivided segments.
 46. Apparatus for generating a perspective view display of a three-dimensional object on a two-dimensional raster scan device comprising: a. object creation means for producing a first set of electrical signals defining surfaces of the object to be displayed; b. means responsive to said first electrical signals for generating a second set of electrical signals related to data defining segments of the surfaces existing along scan lines of the display; c. means responsive to said second set of electrical signals for comparing the relative depths of the segments existing within sample spans selected along scan lines of said display device to determine if more than one segment is visible within the selected sample spans; d. means responsive to the condition wherein more than one visible segment is determined to exist for selectively subdividing the sample spans; e. a display device; and f. circuit means connected connected between said display device and said depth comparison means and said subdividing means for displaying the segments determined to be visible within the sample spans and the subdivisions thereof.
 47. Apparatus of claim 46 wherein the depth comparison means comprises: means for selecting left and right clipping points defining at least a portion of the sample span; means for successively subdividing the segments relative to the selected clipping points; and means comparing the relative depths of the subdivided segments after each successive subdivision.
 48. Apparatus of claim 47 together with means responsive to signals from said depth comparison means for successively subdividing the segments until a predetermined relationship exists between the clipping points and the subdivided segments, or until it is determined that only one visible segment exists between the clipping points.
 49. Apparatus of claim 46 wherein the sample spans extend between two sample points selected along the scan lines and further comprising means responsive to the condition in which more than one segment is determined to be visible within a sample span for selectively subdividing said span by moving the rightmost sample point of said span to coincide with the leftmost segment edge existing between the sample points when at least one segment edge exists therebetween.
 50. Apparatus of claim 49 further having means responsive to a condition wherein a sample span within which two segments are determined to be visible and no segment edges exist for selectively subdividing said span by calculating the point of intersection between the two segments and moving the rightmost sample point to coincide with the calculated point of intersection.
 51. Apparatus of claim 50 further having means responsive to the conditioN where a sample span has more than two segments which are determined to be visible and no segment edges exist for selectively subdividing said span by moving the rightmost sample point to coincide with the mid-point of the sample span.
 52. A system operating in real time for converting stored input data into output data, said input data describing the surfaces of a three-dimensional object, said output data describing only the visible surfaces of the object projected onto a two-dimensional view plane established according to the desired orientation of the object, said system comprising: a. a display device wherein the display is produced on a view plane via a predetermined number of vertically spaced, substantially horizontal lines; b. means for generating segment data defining segments of the projected surfaces existing between edges of the projected surfaces along each horizontal line; c. means selecting a predetermined number of sample points along each horizontal line; d. means determining the number of visible segments existing between the selected sample points including means for comparing the relative depths of the segments as measured in a direction perpendicular to the view plane that exists between selected sample points along each horizontal line; e. means in response to the condition wherein more than one visible segment exists between the selected sample points for selectively subdividing the portions of the horizontal lines that are defined by the selected sample points; f. means responsive to the condition when the relative depth comparison means indicates that only one segment is visible between the sample points or the subdivisions thereof for generating output data defining a visible segment; and g. circuit means for connecting signals from said output data generating means to said display device.
 53. In a system for generating a perspective view display of a three-dimensional object on a two-dimensional raster scan display device from input data defining surfaces of the object converted into projected surface data representing the surfaces of the object projected onto a two-dimensional view plane established according to the desired orientation of the object by apparatus including means for determining which of the surfaces represented by the projected surface data are to be displayed, and means for modifying the brightness of the display according to the projected surface data representing the surfaces determined to be displayed, the improvement wherein the surfaces to be displayed are determined and displayed in real time for each frame of the raster scan display device by apparatus including: means for generating edge data in the form of electrical signals from the projected surface data, the edge data representing edges of the projected surfaces; means responsive to the edge data electrical signals for generating segment data electrical signals defining continuous segments of the projected surfaces existing along each scan line; means responsive to the segment data electrical signals for comparing the relative depths of the segments defined by the segment data along each scan line to generate visible segment data signals; and means responsive to the visible segment data electrical signals for modifying the brightness of the raster screen display.
 54. In apparatus for determining the relative visibility of two line segments projected onto a predetermined two-dimensional view plane along a line of intersection between the view plane and a plane perpendicular to the view plane, said line segments being coplanar and lying in a plane perpendicular to the view plane, each of said line segments being specified by two X end values specified in the view plane and two Z end values specified in the plane perpendicular to the view plane; circuit means for selecting a sample span between two sample points along said line of intersection; means for comparing the relative depths of the lIne segments existing between the sample points to determine which line segment is visible between the sample points; means selecting a new sample span by moving the next sample point to coincide with the right sample point and for selecting a new right sample point; means for storing signals corresponding to the visible portions of said line segments; and means for utilizing said visible portions in a display.
 55. Apparatus as defined in claim 54 further having means comparing the X end values of line segments with the values of said sample points to determine if any of said X values lie between said sample points; and means responsive to the condition where an X end value is determined to exist within said sample span for moving the rightmost sample point in said sample span to coincide with the leftmost X end value of said line segments existing within the selected sample span. 